The subject matter disclosed herein relates to elevator systems driven by belts. More specifically, the subject disclosure relates sheave configurations from elevator systems driven by belts.
Elevator systems utilize one or more belts, such as coated steel belts operably connected to an elevator car, and driven by a motor to propel the elevator car along a hoistway. Coated steel belts in particular include a plurality of wires located at least partially within a jacket material. The plurality of wires is often arranged into one or more strands and the strands are then arranged into one or more cords. In an exemplary belt construction, a plurality of cords is typically arranged equally spaced within a jacket in a longitudinal direction.
The motor drives a sheave, in this case a traction sheave, over which the coated steel belt is routed. The belt gains traction at the traction sheave, such that rotation of the traction sheave consequently drives movement of the elevator car. The system may further include other sheaves around which the coated steel belts are routed to change direction of the coated steel belt. In some systems, the roping arrangement of belts is such that sheaves are used to rotate or twist the belts as required. For example, as shown in FIG. 9, is a single belt 100 system the sheaves 102 may be arranged as shown such that a pure twist of the belt 100 is achieved, with no draw of the belt 100 between sheaves 102. Referring now to FIG. 10, in systems with multiple, parallel belts 100, for example, two belts 100, the sheave 102 arrangement imparts draw, as well as twist between the sheaves 102. The arrangement produces pure twist in one belt 100, while also producing twist and draw in the other belt 100. The draw results in tracking problems for the belt 100, causing the belt to move laterally on a sheave crown 104 and hit flanges 106 of the sheave. This causes excessive wear on the belt 100, especially at edges thereof, and also causes belt-sheave noise and uneven stress on the belt 100 which leads to premature belt 100 failure.
Further, in some systems, one sheave pair 108 is at a fixed location in the hoistway, while the other sheave pair 110 is located at an elevator car. As the elevator car moves in the hoistway, the distance between sheave pairs 108 and 110 changes, so that the draw angle also changes. For example, as the sheave pairs 108 and 110 move closer together, the draw angle increases, Tracking deviation is therefore not constant, and becomes more severe as the sheave pairs 108 and 110 move closer together.